1. Field of the Invention
The invention relates to a transmitter as well as a transmission method which are particularly high-performance. The invention also relates principally to a receiver.
2. Discussion of Background
It is known to transmit ion by using modulated waves, such as, for example, electromagnetic waves. It is known to try to increase the transmitted information throughputs. However, the increase in the throughput more often than not comes through an increase in the band of frequencies used. Now, in the case of guided transmissions there is a limitation due to the passband of the channel, for example a coaxial cable or an optical fibre, whilst in transmissions over the air there are no longer sufficient frequencies to satisfy all the needs.
Moreover, the Patent Application FR 86 09622 published under the No. 2,601,210 describes a method of transmission using symbols A (f, t) . Each symbol corresponding to a frequency and a given transmission time. The transmission time not being fixed, the device does not use any means of fine synchronization, which thus limits the spectral response to approximately 0.7 bit/(Hz.s). Moreover, the French certificate of addition 86 13271 published under the No. 2,604,316 describes the use of devices for calculation of the discrete Fourier transform for the demodulation of the signal. This certificate of addition suggest moreover the use of a guard period between the symbols. However, the nonorthogonality of the channels used limits the spectral response, in the best of cases, to 1 bit/(Hz.s).
With the device according to the present invention, it is possible to exceed 5 bits/(Hz.s) under analogous conditions.
The present invention relates to an improvement in the means and of transmission methods described in the Patent 86 13937; 86 13938; 86 13939; 86 13940; 86 13941; 86 18351; 86 18352.
In the devices of known type it has often been tried to increase the information throughput by decreasing the transmission times allocated to each information unit, (or by increasing the number of possible symbols). Thus, a broadened spectrum was generated, whose secondary lobes have to be filtered on transmission, thus creating a distortion in the signal. For a square signal with a period .tau. a spectrum possessing numerous secondary lobes is obtained; the principle has a width of 2/.tau.. In the remainder of this specification this distortion in the signal is called auto-distortion.